Protease

A protease is an enzyme that breaks the peptide bonds linking amino acids in proteins. Proteases digest food, trim newly made proteins into their active form, and regulate processes from blood clotting to cell death.

Proteases are classified by the chemistry of their active site. Serine proteases, such as trypsin and chymotrypsin, and cysteine proteases use a nucleophilic residue to attack the bond, while aspartic proteases such as pepsin and metalloproteases use water activated by acidic residues or a metal ion like zinc. Many are made first as inactive precursors called zymogens, which prevents them from damaging the cell that produces them.

Digestive proteases break food proteins into peptides and amino acids. Caspases, a family of cysteine proteases, carry out apoptosis, clotting factors form a protease cascade, and the proteasome destroys proteins marked for disposal. Furin, a protease of the Golgi, activates many hormones and also the spike proteins of some viruses, as described under furin.

Blocking a protease can stop a pathogen. The protease of HIV cuts viral polyproteins into working parts, and protease inhibitors were an important part of combination therapy from 1995 onwards. Drugs against hepatitis C and COVID-19 target viral proteases, and angiotensin-converting enzyme inhibitors treat high blood pressure. Their activity is studied in proteomics and in biochemistry.

• Enzymes — the class of molecules they belong to
• Peptide Bonds — what they cut
• HIV — a virus whose protease is a drug target